In the last few years, much attention has been paid to very precise surface topographical mapping performed using so-called "tunneling" techniques, referred to as scanning tunneling microscopy ("STM"). The pioneering work was done by Binnig et al and has been widely publicized. In this technique, an extremely sharp probe, having a point on the order of atomic dimensions in radius, is closely juxtaposed to a surface to be imaged. When the probe approaches the surface to within a few nanometers and a small electric potential is applied therebetween, a tunneling current flows therebetween, even though there is no direct contact. The resistance of the tunneling junction thus formed varies exponentially with the spacing of the point from the surface. If the probe is scanned over the surface while the probe-to-surface spacing is controlled by a servo loop arranged to maintain the tunneling current constant, the probe will be moved up and down away from the nominal plane of the surface in a manner corresponding to the surface topography. Accordingly, variations in the servo control signal are directly responsive to variations in the surface topography and can be used to image the surface.
The principle of detecting a tunneling current and using it to measure distance has been employed in controlling the height of a conventional inductive read/write head from a magnetizable medium in U.S. Pat. No. 4,853,810 to Pohl et al.
In U.S. Pat. No. 4,831,614 to Duerig et al, variations in tunneling current are used to read and write data to a storage medium. The preferred embodiment of the Duerig et al device appears to involve the trapping of electrons in the medium rather than variation in the local magnetic characteristics thereof per se. See column 2, line 62--column 3, line 2. In Duerig et al a plurality of scanning tips arranged in an orthogonal array are disposed in close juxtaposition to a storage medium which is disposed on the end of a cylinder of piezoelectric material. The piezoelectric material is driven such that the storage medium rotates circularly with respect to the stationary read/write tips. Accordingly, the medium effectively circles around each of the individual read/write tips, each having an individual circular storage area.
By comparison, in the Pohl et al patent, the medium and the head are themselves conventional and the tunneling electrode is merely used to control their spacing.
In both Pohl et al and Duerig et al the head is rigidly mounted and there is no compliance intended in the head mounting arrangements.
In Quate U.S. Pat. No. 4,575,822, data is stored on a substrate by perturbing its electrical or physical characteristics. The data is then read by scanning a tunneling probe over the surface and measuring variations in the tunneling current. Quate does not suggest that the tunneling probe should be compliant.
In Hobbs et al, "Magnetic Force Microscopy with 25 nm Resolution", Applied Physics Letters, 55(22) (1989), in Goddenhenrich et al, "Investigation of Bloch Wall Fine Structures by Magnetic Force Microscopy", Journal of Microscopy, 152(2) (1988), and Rugar et al, "Magnetic Force Microscopy: General Principles and Application of Longitudinal Recording Media", Journal of Applied Physics 68, 1169-1183 (1990), related magnetic force microscopy (MFM) techniques are disclosed. In MFM, localized variations in surface magnetic characteristics of members are imaged by detecting variations in magnetic force between a probe comparable to a tunneling probe and a substrate. In the Goddenhenrich et al paper, the probe is oscillated by a piezoelectric oscillator and variations in its resonant frequency due to variations in the local magnetic field are used to "map" the magnetic field. It is disclosed in Goddenhenrich et al that conventional scanning tunneling microscopy techniques can also be used to map the surface topography, and these maps can be compared to measure any correlation between variations in the local magnetization and the surface topography. See the paragraph extending between pages 529 and 531 of the Goddenhenrich paper.
In the Hobbs et al paper, a magnetic member closely juxtaposed to a sample is driven at frequencies varying slightly from the resonant frequency of the tip/drive system. Any change in the force existing between the tip and the sample alters the resonant frequency and can thus be detected to determine atomic and magnetic forces. The distance between the tip and the substrate is measured optically using complex interferometric techniques. PG,5
In Saenz et al, "Observation of Magnetic Forces by the Atomic Force Microscope", J. Appl. Phys. 62(10), (1987), there is discussed an atomic force microscope wherein a sharp tip attached to a tiny cantilever is used to map the contours of the sample. The atomic forces between the tip and the sample are detected by measuring the deflection of the lever. This publication also teaches that magnetic forces can be measured with the same apparatus.